There are various kinds of devices, including fans, which are driven by a motor to operate. Therefore, the quality of the motor determines the quality of the device using same. Among others, the bearing is an element that has most important influence on the motor operation. The bearing that fails to lubricate and hold the rotary shaft of the motor in place will produce noise during motor operation or even shortens the motor service life in a worse condition.
To enable sufficient lubricating effect, the bearing for fan is usually an oil-impregnated bearing received in a bearing cup made of a metal material, such as copper. The metal bearing cup is processed by turning and has relatively high precision, so that the oil-impregnated bearing can be easily and properly fitted in the metal bearing cup by way of press fit. Meanwhile, it is also easier to control the tightness of a copper ring that is arranged in the bearing cup by tight fit to locate above the oil-impregnated bearing. The copper ring holds down the bearing in the bearing cup and prevents the bearing from moving out of the bearing cup when it rotates along with the fan's rotary shaft, so that the fan can operate stably.
While the metal bearing cup has the advantage of allowing easy control of the accurate fit between it and the copper ring and the oil-impregnated bearing, it has relatively complex structure and involves complicated processing procedures. When the metal bearing cup has to be additionally turned for forming a stepped inner wall surface for supporting the oil-impregnated bearing thereon, or when the metal bearing cup has an inner diameter too much different from the outer diameter of the oil-impregnated bearing, additional turning is required to expand the inner diameter of the metal bearing cup until an allowable tolerance between the bearing cup inner diameter and the bearing outer diameter is reached. In this case, the overall manufacturing cost of the fan is inevitably increased.
The bearing cup in conventional fans can also be integrally formed of a plastic material by injection molding for use with the oil-impregnated bearing. A copper ring is also provided in the plastic bearing cup above the oil-impregnated bearing for holding down the bearing, so that the bearing is prevented from moving out of the bearing cup when it rotates along with the fan's rotary shaft and the fan can operate stably. While the plastic injection molded bearing cup can be manufactured at lower cost compared to the metal bearing cup, it has its own problem. That is, the bearing cup integrally formed by injection molding tends to have an inner diameter with a relatively large size tolerance, which results in difficulty in well control of the tightness of the copper ring in the bearing cup. When the inner diameter of the injection molded bearing cup is too large, the copper ring is loosely fitted in the bearing cup and fails to effectively hold down the oil-impregnated bearing and prevent the same from moving out of the bearing cup. On the other hand, when the inner diameter of the injection molded bearing cup is too small, different structural damages tend to occur, such as a broken bearing cup and a deformed or shrunk oil-impregnated bearing.
Therefore, the conventional fans, either having a metal bearing cup or a plastic injection molded bearing cup, all have a copper ring for holding down the bearing in the bearing cup to ensure stable fan operation. However, with the trend of designing and manufacturing slim-type electronic products, such as notebook computers, miniature cooling fans having reduced overall thickness are also developed to match the slim-type electronic products.
The conventional miniature fans have a metal or a plastic bearing cup that can receive an oil-impregnated bearing therein but not the copper ring. This is because the currently available technique fails to manufacture a copper ring that can match the size of the bearing cup of the miniature fan. Therefore, the existing miniature fans do not have a copper ring mounted in the bearing cup thereof. As a result, when the miniature fans operate, the oil-impregnated bearing thereof tends to slide in the bearing cup to produce noise, shorten the fan service life, and adversely affect the fan rotational efficiency.
It is therefore tried by the inventor to develop a laser-welded joint structure between insulation frame and bearing cup of fan to solve the problems and disadvantages in prior art fan structures.